The present invention generally relates to seatbelt retractors and in particular relates to inertial sensors utilized therein.
A typical seatbelt retractor is designed to be installed within a vehicle at a fixed position such as on the B-pillar or attached to a non-rotatable portion of the seat frame. The seat belt retractor has an inertia sensor or a vehicle sensor, which responds to changes in horizontal vehicle acceleration. The conventional inertia sensor includes a housing having a support surface, an actuator lever, and an inertia mass such as a standing man, ball or weighted member with a lower spherical surface. During non-accelerating or non-decelerating conditions, the inertial mass is at a nominal, typically vertical position aligned to the local gravity vector. The inertia sensor is sensitive to vehicle deceleration. Upon reaching a triggering deceleration, the inertia mass moves upon the support surface and as it does, changes its elevation thus engaging the lever arm. The lever arm or locking pawl is raised into engagement with another retractor part, typically the teeth of a ratchet wheel thus initiating the locking of the retractor spool and preventing further payout of the seatbelt webbing.
The triggering deceleration sensitivity of an inertia sensor is the magnitude of deceleration that will trigger the inertia sensor. The triggering of the inertia sensor is an event whereby the inertia mass moves, which initiates the locking mechanism of the seatbelt retractor. The triggering deceleration sensitivity is measured in acceleration units such as gravity (g), and when a threshold amount of deceleration is reached, the inertia sensor is actuated.
In addition to the inertia sensor being sensitive to deceleration, the sensor is also sensitive to the tilting angle of a vehicle. The tilting of a vehicle brings about a tilting of the seatbelt retractor. If the tilting angle of the vehicle exceeds a threshold, the inertia sensor will actuate. Generally speaking, the more sensitive the inertia sensor is to deceleration, the more sensitive the inertia sensor will be to the tilting angle. In designing an inertia sensor to be unaffected by tilting of 15 degrees in any direction, the minimum value for the triggering deceleration sensitivity is 0.27 g. Thus, in order to prevent the seatbelt retractor from locking under tilting angles of 15 degrees or less, the triggering deceleration sensitivity needs to be 0.27 g or greater. This minimum threshold for triggering deceleration sensitivity presents a problem for the early stage of a braking event that has a low deceleration onset rate such as 0.4 g/s. A deceleration onset rate is defined as the initial rate of deceleration change of a vehicle during braking or a crash. The lower the deceleration onset rate, the longer the time that is required for the deceleration to reach a triggering deceleration level. A long amount of time translates to a significant forward movement of an occupant during the braking event. Under a braking event that has an acceleration onset rate of 0.4 g/s, it will take more than 0.6 seconds for the acceleration to reach a triggering level of 0.276 g and during this time period the occupant will move forward more than 74 mm.
Due to the fact that the tilting angle affects the lower limit on the triggering deceleration sensitivity, there is a need to develop an inertia sensor that is not influenced to changes in tilting.
The inertia sensor in accordance with the present invention has an inertia sensor consisting of two inertia bodies connected in a way that the two inertia bodies form a 360 degree double pendulum system. The inertia sensor has a self-compensating feature and also senses deceleration. Due to the self compensating feature, the inertia sensor in the present invention is not triggered when the vehicle is subjected to tilting angles of 30 degrees or less. Even though the inertia sensor is not triggered during vehicle tilting, the inertia sensor is triggered during predetermined amount of deceleration.
The inertia sensor in the present invention comprises a primary mass, a secondary mass, and a lifter. The primary mass is responsible for conferring the benefit of the self compensating function on the inertia sensor, while the secondary mass is responsible for triggering the inertia sensor in the event of deceleration. During a braking event or a crash, there is relative angular displacement between the primary mass and the secondary mass resulting in the secondary mass pushing the lifter, which rotates a locking pawl. The rotation of the locking pawl initiates the locking mechanism of the seatbelt retractor.